This disclosure pertains to methods and systems for enhancing or improving the recovery of oil and gas from hydrocarbon formations, both conventional and unconventional hydrocarbon formations, and is particularly effective for formations with low permeability.
Tight oil, also referred to as light tight oil (LTO) or shale oil, and gas condensate contain light crude oil present in a petroleum-producing formation that has low permeability. The formation may be shale or tight sandstone, and the fluid flowing in the formation may be in the liquid or gas phase. Unlike more conventional sources in which oil and gas flow naturally and can be pumped to the surface without external stimulation, production of tight oil is considered unconventional and typically requires additional interventions such as hydraulic fracturing. It has been demonstrated that multiple transverse fracture horizontal wells (MTFHWs) can produce oil and gas from formations with lower permeability than was profitable to produce from before the application of this well technology. Originally developed for shale gas, application of this well design has enabled the U.S. industry to increase domestic oil production by about 4.5 million barrels per day in the 5 years from approximately 2010 to 2015.
One problem with the current design of multiple transverse fracture horizontal wells (MTFHW) is that they typically only support primary production. During primary production, reservoir pressure is usually sufficient to flow the oil and gas to the surface. Over the lifetime of a well, the pressure will fall until it is no longer sufficient for profitable recovery of the petroleum product. Secondary production then requires the introduction of pressure support in order to flow the oil and gas to the surface. Often this is done through the injection of fluids such as water, specialty chemicals such as enhanced oil recovery (EOR) polymers, solvent, and/or a gas. The injected fluids increase pressure in the formation again, ideally causing the flow of additional oil and gas to the surface through one or more production wells. However, in MTFHW, attempts to supplement pressure for secondary production by using water injection have been commercially unsuccessful. The likely reason is that injected fluid finds a flow path in the created primary and secondary fractures and bypasses most of the oil and gas remaining in the formation. When the injected fluid enters a producing wellbore, this is known as breakthrough. Early breakthrough is a problem in MTFHW due to the interconnection of fractures and the difficulty in applying pressure across the unfractured matrix where oil and gas remains unproduced.
What is needed, therefore, is a method for improving recovery of hydrocarbons using hydraulic fracturing that allows not only for primary production but also for extended secondary production.